The influence of micrometeorlogical factors on air quality within urban
street canyons

Andrew Jackson

Summary

A pollution monitoring and modelling study has been carried out on a
low street canyon (height to width ratio = 0.53) in a suburb of Leeds,
Headingly with the aim of determining the micrometeorological influences
on pollution concentrations and dispersion. Pollution monitoring
was carried out under a variety of meteorological conditions, over ten
separate days using a mobile atmospheric unit and measurements were taken
for five pollutants, NO, NOx, CO, O3 and NO2,
along with three meteorological variables, wind direction, wind speed and
temperature.
Two models have been employed to simulate the flow, turbulence and
concentration fields within the canyon: the CFD model code, Fluent and
the empirical air quality management package, Airviro.

Results

The results showed

synoptic conditions control ambient pollution levels

There was poor correlation between pollution concentrations and meteorological
parameters and traffic flows in the canyon.

The Fluent model predicted a transitional flow regime, between Wake- Interference
flow and isolated roughness flow within the canyon. This was an unexpected
result

The highest turbulent Kinetic energy values were predicted to be found
at roof level.

Fluent and Airviro both over predicted CO concentrations when comparing
their output to specific days. The discrepancy was greatest at the
windward.

Airviro over predicted NOx concentrations by a large amount.

This study highlights the need for extensive experimental data, with
measurements made at both side walls, from the base of the canyon up to
the roof level, so that numerical models such as fluent can be correctly
validated.